[pulseaudio-discuss] snd_pcm_avail no reliable

[Raymond Yau]

>>
>>  >
>>  >   below is what the terminate shows when running pcm_avail.c
>>  >
>>  >   uid=0 gid=1007 at nutshell:/ # alsactl_test
>>  > min_period_size: 8 frames, dir: 0
>>  > Playback hwparams: FIFO size is 8
>>  > Hardware PCM card 0 'rsnd-dai.0-dirana3.0' device 0 subdevice 0
>>  > Its setup is:
>>  >   stream       : PLAYBACK
>>  >   access       : RW_INTERLEAVED
>>  >   format       : S16_LE
>>  >   subformat    : STD
>>  >   channels     : 2
>>  >   rate         : 48000
>>  >   exact rate   : 48000 (48000/1)
>>  >   msbits       : 16
>>  >   buffer_size  : 4096
>>  >   period_size  : 1024
>>  >   period_time  : 21333
>>  >   tstamp_mode  : NONE
>>  >   period_step  : 1
>>  >   avail_min    : 1024
>>  >   period_event : 0
>>  >   start_threshold  : 1024
>>  >   stop_threshold   : 4096
>>  >   silence_threshold: 0
>>  >   silence_size : 0
>>  >   boundary     : 1073741824
>>  >   appl_ptr     : 0
>>  >   hw_ptr       : 0
>>  > Playing silence
>>  > Available: 0, loop iteration: 0
>>  > Available: 1024, loop iteration: 1469
>>  > Available: 2048, loop iteration: 5609
>>  > Available: 3072, loop iteration: 9667
>>  >
>>  >  All I got is just the 4 lines.
>>
>> If your sound card only increment hw_ptr only at interrupt occur, you
>> need to increase default_rewind_safeguard from 256 bytes to your
>> selected period size
>
>
> No. PulseAudio, in timer-scheduling mode, does not use periods at all.
You need to change the driver so that it reports SNDRV_PCM_INFO_BATCH, so
that PulseAudio does not try to use this mode.
>
>
>>
>> This mean that  your sound card won't work with timer scheduling or
>> dynamic latency, you can only archieve low latency by decrease period
size
>> Why do pulseaudio enable timer scheduling when most sound card use IRQ ?
>
>
> Because most broken sound cards driver authors forget to report
SNDRV_PCM_INFO_BATCH?
>

Most driver use irq interrupt , only a few sound cards ( seem less than
ten) can report   DMA_RESIDUE_GRANULARITY_BURST

Why do timer based scheduling enablef by default ?
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